1. Field of the Invention
The present invention generally relates to lenses. More specifically, the present invention provides lenses having multiple vision zones with reduced distortion and reduced visibility of any included discontinuities.
2. Background Art
Multifocal lenses generally have two or more adjacent regions of different optical power to provide multiple vision zones. Examples of traditional multifocal lenses include bifocals, trifocals, and progressive addition lenses. The multiple vision zones of a multifocal lens allow a wearer to more clearly view differently spaced objects using different vision zone correction prescriptions. A typical wearer of a multifocal lens may have a first vision correction prescription for viewing distant objects and a second vision correction prescription for viewing near objects.
Many multifocal lenses are lined lenses. That is, many multifocal lenses have a discontinuity separating each vision zone that can be seen by someone looking at a wearer of the lens. As a result, many individuals find lined multifocals to be cosmetically unappealing. Additionally, a wearer of a lined multifocal lens will perceive the effects of traversing the multiple discontinuities when the wearer's line of sight crosses the boundaries of the vision zones. The traversal of any such discontinuity can cause an image jump perceptible to the wearer. Experiencing an image jump can be visually disturbing and distracting to the wearer. Accordingly, experiencing multiple image jumps in a multifocal lens that provides two or more vision zones exacerbates the discomfort of the user.
Blended multifocals can reduce the effects of the abrupt discontinuity between two adjacent regions of different optical powers. Generally, a blend zone is provided between the two different optical power regions to provide a relatively smooth transition from the optical power of the initial zone to the optical power of the adjacent zone. Such blending can improve the aesthetics of a multifocal lens by reducing the visibility of the discontinuity between the adjacent regions. However, blend zones are typically unusable portions of a lens due to poor resulting optics associated with the blend zone. Therefore, using a blend zone to reduce the visibility of an optical discontinuity can reduce the usability of the vision zones of a multifocal lens by reducing their size. Further, blend zones can introduce their own unique disturbances as experienced by a wearer when traversed by a wearer's line of sight. Such disturbances can be introduced by the blending of the optical power which can create unwanted astigmatism and distortion across the blend zone.
Due to the disadvantages of traditional multifocals (lined or blended), many individuals opt to wear multiple pairs of spectacle lenses or choose to wear a progressive lens. Progressive lenses generally provide a smooth continuous change in optical power between different regions of a lens. While many individuals find progressive lenses to be more appealing cosmetically, they too are often accompanied by many disadvantages. For example, many progressive lenses have narrow channels or vision zones, cause wearers to experience an unpleasant visual motion known as swim, and have large amounts of distortion (e.g., unwanted astigmatism) in the periphery of the lens.
Many prior art lens designs have attempted to improve upon the deficiencies of traditional multifocal lenses yet continue to suffer from significant drawbacks. FIG. 11 illustrates a front and side view of a prior art multifocal lens design described in U.S. Pat. No. 6,270,220 to Keren. Keren describes a multifocal lens having a progressive region 1104 and a diffractive segment 1102. The diffractive segment 1102 can be on the front or back surface of the multifocal lens. The multifocal lens is made up of a single material and comprises a single layer. The diffractive segment 1102 is limited to being positioned over the intermediate region of the progressive region 1104 only. The diffractive segment 1102 does not contribute optical power to the far distance or near distance vision zones of the multifocal lens. Instead, the diffractive segment 1102 contributes multiple different optical powers to the intermediate region only. The multiple different optical powers are not additive and can make the intermediate region uncomfortable to a wearer. Overall, the multifocal lens described in Keren provides only three vision zones with only two vision zones (the near vision and the distance vision zones) being stable.
FIG. 12 illustrates a front and side view of a prior art multifocal lens design described in U.S. Pat. No. 4,461,550 to Legendre. Legendre describes a multifocal lens having a progressive region 1202 and a refractive segment 1204 superposed in the near vision zone of the progressive region 1202. The refractive segment 1204 can be placed on top of the multifocal lens or can be positioned within the multifocal lens. The refractive segment 1204, when buried, does not form a separate layer of the multifocal lens. The refractive segment 1204 introduces a discontinuity 1206 around the near vision zone which can be very disturbing to a wearer. The refractive segment 1204 does not contribute to the optical power provided in the intermediate or far distance vision zones of the lens. Due to the increase in near vision power from the superposed refractive segment 1204, the power ramp up of the intermediate region of the progressive region 1202 must be increased significantly. As a result, unwanted astigmatism is increased in the lens thereby reducing the sizes of the vision zones. Further, the multifocal lens described in Legendre provides only three vision zones of which only two vision zones (the near vision and distance vision zones) are stable.
FIG. 13 illustrates a front and side view of a prior art lens design described in U.S. Pat. No. 5,305,028 to Okano. Okano describes a multifocal lens having a fused segment that has a first spherical segment 1302 and a second spherical segment 1306 joined by a progressive region 1304. The boundaries between the progressive region 1304 and the spherical regions 1302 and 1306 are transition regions 1308. These transition regions 1308 operate similarly to blend zones and therefore restrict the usefulness of the transition regions 1308 optically. The multifocal lens of Okano comprises a single material. Further, the multifocal lens of Okano comprises multiple discontinuities which can be very discomforting to a wearer of the lens when the wearer's line of sight traverses the provided vision zones. The near vision zone of the multifocal lens described by Okano comprises the spherical region 1306 only such that the progressive region 1304 does not contribute to the total near add power of the lens.
FIG. 14 illustrates a front and side view of a prior art lens design described in U.S. Pat. No. 6,086,023 to Blum et al. Blum et al. describes a multifocal lens having a progressive region 1404 and various discontinuous elements 1402. The progressive region 1404 is limited to being placed on a perform lens 1406. Further, the multifocal lens is limited to having two or more of the discontinuous optical elements 1402 added to the perform 1402. Blum et al. provides multiple vision zones but at the cost of introducing multiple discontinuities which results in significant discomfort for the wearer. Further, Blum et al. places the discontinuous elements below the start or top of the progressive region 1404. The discontinuities are therefore positioned in close proximity with one another which can exacerbate the discomfort of the wearer. As a result, the lens described by Blum is not viable for use when working on a computer.
Accordingly, what is needed is a lens that overcomes one or more deficiencies of prior art lenses. More specifically, a lens that provides multiple vision zones with low distortion and a minimum number of optical discontinuities while simultaneously remaining cosmetically pleasing is desired.